1. Field of the Invention
The present invention relates to a physical-quantity detecting device provided with a sensor chip which is subjected to action of force and outputs a corresponding signal. The physical-quantity detecting device according to the present invention can be applied, for example, in a semiconductor-type acceleration detecting device which is subjected to acceleration and detects the applied acceleration by a displacement of a cantilever formed on a silicon substrate.
2. Related Arts
A conventional structure of an acceleration detecting device is indicated in FIGS. 13A and 13B.
FIG. 13A is a sectional side view of an acceleration detecting device having a housing 100 in which a cover 100a is formed interiorly with a hollow portion. A sensor chip to detect acceleration, processing circuit and the like are housed within the hollow portion thereof. This housing 100 has a cover 100 for fixing use having screw holes, and is fixed to a fixing plate 103 by screws 102. The fixing plate 103 has an L-shaped configuration and is fixed to a circuit board 104 by a screw 103a. Consequently, the housing 100 comes to be mechanically fixed substantially perpendicularly to the circuit board 104 via the fixing plate 103.
Furthermore, the housing 100 has a terminal 101 connected with electrical circuitry disposed in an interior thereof. This terminal 101 is connected to an output terminal 105 which is soldered to the circuit board 104 and electrically connected to wiring on the circuit board 104. The output terminal 105 is positioned and fixed by a molded-resin portion 106.
FIG. 13B indicates a plan structure of the housing 100 with the cover 100a detached. As shown in FIG. 13B, a processing circuit 109 composed of chip components such as a sensor chip 108, processor chip, resistor, and capacitor is formed on a ceramic substrate 107 within the housing 100. This processing circuit 109 detects displacement due to acceleration of the sensor chip 108 and outputs an acceleration signal. This acceleration signal is sent via the terminal 101 and output terminal 105 to an ECU (Electrical Control Unit, not illustrated) on the circuit board 104, and is employed to control an airbag or the like.
FIG. 14 indicates a structural sectional schematic of the foregoing housing 104. The ceramic substrate 107 is fixed by adhesive to a stem 110, and the sensor chip 108 and processing circuit 109 are formed on this ceramic substrate 109. A metallic cover 100a is installed by welding on a front side of the stem 100, airtightly sealing a hollow portion 111. Additionally, a metallic cover 100b is installed by welding on a rear side. The sensor assembly is structured thereby.
The terminal 101 and the sensor chip 108 and processing circuit 109 are wire-bonded by wires 112 and electrically connected with an exterior. The terminal 101 is hermetically sealed with respect to the step 110 by low-melting glass 113, and the cover 100a is welded to the stem 110 and the housing 100 interior is airtightly sealed.
Because the circuit board 104 indicated in FIG. 13A is installed on a plane parallel to a floor of a vehicle passenger compartment, the housing is installed via the fixing plate 103 substantially perpendicularly to the circuit board 104 so that the sensor chip 108 comes to be substantially perpendicular with respect to the circuit board 104.
With the conventional acceleration detecting device, there exists the problem wherein the components are many and structure as well is large and complex, and consequently the number of fabrication steps is also large.
That is to say, in the above-described conventional structure, the cover 100a, stem 110, and terminal 101 are provided as the structure of the portion to seal airtightly. Furthermore, disposal of the fixing plate 103 fixed substantially perpendicularly to the circuit board 104 as well as the cover for fixing use 100b and screw 102 for fixing by screw thereto are required to connect the housing 100 substantially perpendicularly with respect to the circuit board 104. Moreover, through-holes for solder use are required for the output terminal 105 and circuit board 104 to electrically connect the circuit board 104 and the acceleration detecting device.